Millions of small-scale farmers around the world irrigate with marginal-quality water, often because
they have no alternative. There are two major types of marginal-quality water: wastewater
from urban and peri-urban areas, and saline and sodic agricultural drainage water and
groundwater. Around cities in developing countries, farmers use wastewater from residential,
commercial, and industrial sources, sometimes diluted but often without treatment. Sometimes
farmers in deltaic areas and tailend sections of large-scale irrigation schemes irrigate
with a blend of canal water, saline drainage water, and wastewater. Still others irrigate with
saline or sodic groundwater, either exclusively or in conjunction with higher quality surface
water. Many of those farmers cannot control the volume or quality of water they receive.
Wastewater often contains a variety of pollutants: salts, metals, metalloids, pathogens,
residual drugs, organic compounds, endocrine disruptor compounds, and active residues
of personal care products. Any of these components can harm human health and the environment.
Farmers can suffer harmful health effects from contact with wastewater, while
consumers are at risk from eating vegetables and cereals irrigated with wastewater. Application
of wastewater has to be carefully managed for effective use.
In contrast to wastewater, saline and sodic water contains salts that can impair plant
growth but rarely contains metals or pathogens. However, it can lead to soil salinization
and waterlogging, which impair productivity on millions of hectares of agricultural land.
Irrigating
successfully with saline or sodic water requires careful management to prevent
near-term reductions in crop yield and long-term reductions in productivity.